A quiet little world on the beach

Look carefully – you can see the shells as well as their siphons. Credit: L. Milideo

A couple of months ago, I had the chance to spend a few days at the beach. It was wonderful for many reasons: I hung out with my family, I got to see the ocean, and I got to spend time on the beach. Lots of things were just as I’d looked forward to.

The salty, fishy smell that stirred the same excitement and anticipation that I remember from childhood as we left the highway and drove through the salt marshes near the shoreline. The too-rare fun of time spent with family. Sunshine and sand.

But the beach, as it turned out, held surprises, too. Walking along the sand with my husband one afternoon, I was looking for pretty shells to collect. This was when I noticed something I’d seen countless times but never paid much attention to before. Lots of little pools had formed a few feet from the water’s edge, where the waves would occasionally wash up far enough to deposit a little water. The larger ones were occupied by shouting, plastic toy-toting toddlers who splashed in these natural kiddy pools for hours.

But the smaller pools, only a couple of feet across, a couple of inches deep, were occupied by a different (though no less vibrant) crowd. As we walked, I noticed movement in one of these little pools and stooped to look. It was filled with tiny clams, and their shells, in countless pastel shades, looked like a handful of beautiful beads dropped into the water.

The shells didn’t stay there, though. As the wave that had filled the pool receded, the shells began to disappear. Suddenly there were fewer, and fewer still, until near the edges there were almost none. As I watched them, I realized they were working their way back into the wet sand at the bottom of the clear pool. Another wave came up, uncovering them once more, and they immediately began to sink back beneath the surface, one miniscule jerk at a time. Each clam that disappeared into the sand left a tiny hole in its place. At the edge of the pool was a porous-looking sandy flat where moments before there’d been a brilliant array of colorful shells. The little polychrome colony was a mass of constant wriggling movement, a whole little world constantly being washed over, exposed, and reburying itself there on the beach.

The waves crashed. People shouted in the water. Radios played along the beach. And the shell-world happened without a sound.

You can really see their siphons in this one! Credit: L. Milideo

So why does this matter? First of all, because it’s a part of nature, and that’s important. The shells belong to a tiny type of clam of the genus Donax. You can read more about them hereand here. In a nut(clam?)shell, they’re pretty widespread, living on beaches all over the world. They eat by using a siphon that they stick up into the water, which lets them catch tiny animal and plant matter. What’s really amazing about them is their ability to move and even migrate along the beach. I don’t know about you, but when I hear the word “migrate”, I think about birds, or maybe hoofed mammals. I definitely don’t think of clams, but these little clams can do it. Crazy, right?
If you’d like to learn more about how and why clams move, as well as other fascinating information about them, check out this video.

And if you’re more interested in rocks than animals, don’t leave just yet. Coquina is also a type of sedimentary rock, composed of thousands of these tiny shells and other marine invertebrates, and the sand that surrounds them.

These little clams also play an important rolein the larger environment. They’re eaten by birds, crabs, and fish. And their presence on a beach indicates that the ecosystem in that location is pretty healthy. Furthermore, a study showed that these clams seem to absorb oil spill-related toxins and retained these chemicals for longer than their surrounding sand – so they could helpscientists monitor the amount of pollutants in the environment over a longer time period following an oil spill. For these reasons, coquina clams aren’t just a pretty and fascinating presence on the beach – they’re also an important part of their natural world, and an important source of information to scientists.

So next time you walk outside, keep your eyes open. There might be a little world lying right at your feet, quietly telling the story of the environment around you, and reinventing itself with every passing wave.